1. Field of Invention
The present invention is directed to a method for optimizing the transmission of ATM calls via connection hops in order to avoid the loss of ATM cells when employing the weighted fair queuing scheduling method of transmitting cells according to particular requirements. ATM cells are subjected to a peak bit rate limitation wherein a limitation occurs of the time interval of two read counters which sample the memory elements of a calendar in a cyclical time grid.
2. Description of Prior Art
Information is transmitted in cells in contemporary ATM systems. These cells include a header part as well as an information part wherein connection information is stored in the header part and the useful data to be transmitted is stored in the information part. Actual data transmission occurs in the form of cell streams, which include a plurality of cells being transmitted via connection hops between transmitter and receiver. The requirement may potentially exist to utilize these connection hops in a way such that a number of transmitters would transmit their respective cell streams via the same connection hop.
In order to be able to implement the transmission of these cell streams according to their respective requirements, what are referred to as "scheduling methods" have prevailed in the prior art. Pursuant to such methods, the ATM cells are read out of buffer memories of a scheduler means in a specific sequence. The WEIGHTED FAIR QUEUEING SCHEDULING method may be used as an example of such a scheduling method. This known method is disclosed, for example, in the publication "Virtual Spacing For Flexible Traffic Control", J. W. Roberts, International Journal of Communication Systems, Vol. 7, 307-318 (1994). The individual cell streams have different weighting factors allocated to them according to which an actual transmission event is controlled on an individual connection hop.
What is problematical about this procedure is that many of the scheduling methods, including the weighted fair queueing scheduling method herein described, cannot assure a peak bit rate limitation on the following connection hops. This is required, however, everywhere that cell streams are conducted to nodes with small memories.
German Patent Application Serial No. 37 108 07 proposes a scheduling method by which the cell rates are matched to the transmission capacity of the connection hops. The method disclosed comprises two stages that are implemented in chronological succession. How these stages are fashioned, however, is not disclosed in detail.
Further, European Letters Patent 0 498 092 discloses a method wherein the individual connection transmission bit rate is strictly limited. This means, however, that a further connection setup is rejected. For example, as in the case of overload, a flexible manipulation is thus not possible.